Separation of waxy hydrocarbons from oils by flotation



United States Patent 3,338,816 SEPARATION OF -WAXY HYDROCARBONS FROMOILS BY FLOTATION Paul Albert Tritsmans, Antwerp, Belgium, assignor toSociete Industrielle Belge des Petroles S.A., Antwerp, Belgium, aBelgian joint-stock company No Drawing. Filed Feb. 16, 1965, Ser. No.433,180 Claims priority, application Belgium, Aug. 21, 1964, 43,900,Patent 652,105 7 Claims. (Cl. 208-28) This invention relates to theseparation of waxy hydrocarbons from oils by flotation.

It is known to separate waxy hydrocarbons from oils by cooling in thepresence of solvent and separating the solid wax by filtering. It hasalso been proposed to separate waxy hydrocarbons by flotation. In thisprocess bubbles of gas are passed upwardly through the cooled oil sothat the wax separates as a froth at the top of the oil. This processhas the advantage that no filtering or centrifuging is required and itis, in essence, a simple process. Nevertheless, as far as is known, theprocess has never been developed on a large scale. One possible reasonfor this is that the conditions necessary to achieve satisfactoryflotation, involving as they do interaction of three phases, the liquidoil phase, the solid wax phase and the gas phase, are extremely criticaland that different oils can give markedly different results. Thisdifliculty is, in fact, reflected in earlier attempts to improve theprocess, many of which suggest the need for additional components suchas solvents or surface-active agents to provide the necessary physicalconditions for good flotation.

It has now been found that the process can be operated Without the needfor added components when the feedstock contains at least a proportionof cracked material and when the feedstock viscosity is carefullycontrolled.

According to the present invention, therefore, a process for theseparation of waxy hydrocarbons from oils by flotation in which gas ispassed upwardly through the 'oil cooled to a temperature below its cloudpoint is characterised in that the oil being treated contains at least aproportion of cracked material and in that the oil has a viscosity, atthe separation temperature, of not more than 20 centistokes.

' Without being bound by any theory it is suggested that the crackedmaterial may contain compounds which exert a strong influence on thephysical conditions and. allow the ready coalescence of the gas andsolid phases. Whatever the theory, however, it has been found that quitesmall amounts of cracked material have a marked effec and thatincreasing the amount of cracked material does not lead to a positionwhere the effect becomes overdominant and causes complications inanother direction. The proportion of cracked material may thus rangefrom 0.5 to 100% vol., preferably 2 to 907 The cracked material may bederived from either 3,338,816 Patented Aug. 29, 196 7 material themaximum viscosity may thus be 20 centistokes decreasing to 15 when thepercentage of cracked material is 2%. If necessary a feedstock which hastoo high a viscosity may be diluted with lower-boiling materialpreferably boiling in the kerosine boiling range. This can be either astraight run or cracked petroleum fraction and it has not been foundnecessary to use diluent materials such as the previously proposedconventional solvents used in filtration de-waxing.

Waxy hydrocarbons can cause problems in oils boiling in the kerosine,gas oil and wax distillate range (i.e. 150 to 650 C.) and the processmay be used on any of these feedstocks although with the heavierfeedstocks more diluent will naturally be required to lower theviscosity. It has also been found that the presence of asphalt or othermaterials functioning as pour point depressants is deleterious, even invery small quantities, and their presence should thus be avoided. Thecloud points of the oils being treated may vary over a fairly wide rangeand hence the flotation temperature may also vary. Likely temperatureswill however be in the range 0 F. to 80 F., especially 20 F. to F. Thecloud point of the dewaxed oil will with efficient operation besubstantially equal to the temperature used.

The amount of gas used is not critical and satisfactory results havebeen obtained with a ratio by volume of gas at S.T.P. to oil feedstockof as low as 0.2 and with no indication that this is a limiting ratio.Higher rates are not detrimental although they add little furtherbenefit and a suitable range is thus from 0.1 to 10. Any convenient gasmay be used, for example nitrogen, gases thermal or catalytical crackingand may be of any suitable boiling range within the limits of the rangeof fractions that can be treated. Preferred materials are those derivedfrom catalytical cracking of gas oils or waxy distillates to gasoline,or the kerosine boiling-range fractions from the same process. I

The importance of viscosity'has previously been noted. one priorsuggestion indicating that the viscosity shou ld not exceed 50centipoises at the working temperature, being preferably 25 to 50centipoises. It has now been found that these suggested limits are notsufliciently precise and that the maximum viscosity is 20 centistokes atthe working temperature. The proportion of cracked material in the oildoes have a small effect on the maximum allowable viscosity, causing itto increase with increase in cracked material. With oils which are 10%cracked rich in nitrogen such as flue gas, hydrogen or normally gaseoushydrocarbons. Air is also suitable, but its use may be limited on acommercial scale by safety regulations regarding fire hazard.

The gas 'should naturally pass upwardly through the oil in the form ofbubbles and if necessary it can be introduced into the bottom of theflotation bath through known bubblers and dispersers. It has been found,how ever, that the gas can be introduced quite simply and effectively byinjecting it into the suction side of the pump feeding oil to the bath.Nevertheless, in that case, the pump discharge pressure must not bebelow certain limits, in order to dissolve at least part of the gas inthe oil. Suitable pressures are in the range of 2 to 10 kg./cm.

The rate of flow of the oil into and the withdrawal of dewaxed oil fromthe flotation zone should be adjusted to give a suitable residence timeand these can readily be determined by experiment. In practice residencetimes of upwards of 7 hours have been found suitable.

The cooling of the oil to a temperature below the cloud point ispreferably carried out by cooling a stream of oil which is withdrawnfrom the bath, cooled and recycled, which method of cooling is describedand claimed in Belgian application No. 43,901. This application alsogives details of a suitable apparatus for carrying out the presentprocess.

From the present process one can obtain a dewaxed oil of reduced cloudand pour points and also wax. When in the form of froth at the top ofthe flotation zone the wax may contain significant quantities ofentrained oil. However, much of this oil separates on standing and anyoil still remaining can be further separated by known techniques to givewaxes equivalent in quality to waxes separated for example by filtrationin the presence of solvents. If the wax is not required for specialisedpurposes it may be used, for example, as a high quality catalyticcracker feedstock.

The invention is illustrated by the following examples:

3 Example 1 The following example compares the effect of differentviscosities on the ease of Wax removal by flotation.

The feedstock used had the following inspection data:

Runs were carried out using this oil alone and also using this oildiluted with straight-run kerosine of 170 to 230 C. ASTM boiling rangeto give oils with viscosities of 20, 15, and 10 centistokes at 32 F.

The conditions used for the flotation were:

Temperature of oil F 32 Oil feed rate l./hr Gas feed rate l./hr 50Recycle oil rate l./hr 250 Residence time hrs The gas used was air whichwas injected into the suction side of the oil feed pump.

The results obtained were as follows:

Oil viscosity 50 20 10 Yield of Wax 15 20 Yield of dewaxed oil 85 80 80Properties of dewaxed oil Cloud point, F 78 40 30 30 Pour point, F 70 3525 It will be seen that satisfactory results were only obtained atviscosities of 15 and 10 centistokes and that there is a marked changein the results when altering the viscosity through the relatively smallrange of 20 to 15 centistokes.

Example 2 This example compares the effect of diflerent amounts ofcatalytically cracked material on the ease of wax removal by flotation.

Four blends of gas oil and kerosine were made up to give four feedstockshaving a viscosity of less than 15 centistokes at 32 F. and having anASTM boiling range of 160 to 370 C. They had the following compositionsand inspection data:

Blend Straight run material, percent vol 100 96 0 Cat. cracked material,percent vol 0 4 70 100 Cloud point, F 54 54 62 62 Pour Point, F 50 50 6050 Viscosity at 32 F., cs 14 14 13 12 Sulphur, percent wt 1. 4 14.1.6 1. 7

The straight run matenals were obtained by distillation of Kuwait crudeoil. The conditions used for the flotation Wfi j 4 Temperature of oil F30 'Oil feed rate m. /h 10 Gas feed rate Nm. /h 5 Recycle oil rate -m./h 200 Residence time hrs 40 The gas used was flue gas which wasinjected into the suction side of the oil feed pump.

The results obtained were as follows:

Blend 1 2 3 l 4 Yield of wax 15 20 20 20 Yield of dewaxed oil 80 80 80Properties of dewaxed oil: Cloud point, F 44 30 34 30 Pour point, F 3525 30 20 It will be seen that markedly better results were obtained withblends 2, 3 and 4 with 4% or more of cracked material, the oil havingcloud points reduced from 50 or more to 30 F., the latter beingsubstantially the temperature to which the oil was cooled. With blend 1the cloud point was only reduced to 44 F.

The experiment also shows that all the blends treated containedappreciable quantities of sulphur and that this had no noticeable afiecton the results.

I claim:

1. A process for the flotation separation of waxy hydrocarbons from waxyoils to produce dewaxed oil having reduced cloud and pour points whichcomprises passing a flotation gas upwardly through the waxy oil whichhas been cooled to a temperature below its cloud point, said waxy oilcontaining a proportion of cracked material from 0.5 to volume andhaving a viscosity, at the separation temperature, of not more than 20centistokes with the maximum viscosity range being 20* centistokes whenusing 100% of cracked material to 15 centistokes with 2% crackedmaterial; said gas treatment producing a wax-containing foam layer and adewaxed oil layer, and separating the dewaxed oil layer therefrom havingreduced cloud and pour points.

2. A process as claimed in claim 1 wherein the proportion of crackedmaterial is from 290% vol.

3. A process as claimed in claim 1 wherein the cracked material is theproduct of a catalytic cracking process.

4. A process as claimed in claim 1 wherein feedstock boils within therange to 650 C.

5. A process as claimed in claim 1 wherein the dewaxing temperature isfrom 0 F. to 80 F.

6. A process as claimed in claim 1 wherein the gas feed ratio is 0.1 to1'0.

7. A process as claimed in claim 1 wherein the gas is injected into thesuction side of a feed pump, while maintaining the pump dischargepressure at 2 to 10 kg./cm.

References Cited UNITED STATES PATENTS 2,107,137 2/1938 Adams et al208--33 2,370,453 2/1945 Dons et a1. 208-33 2,719,817 10/1955 Doorn208-37 2,904,496 9/ 1959 Bloch et a1 208-28 FOREIGN PATENTS 945,281 7/1956 Germany.

DANIEL E. WYMAN, Primary Examiner. P. KONOPKA, Assistant Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,338,816 August 29, 1967 Paul Albert Tritsmans It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below Column 1line 14 for "solvent" read solvents line 72, for "10%" read 100% column3, in the last table 1n the column headed "2", line 6 thereof, for "14read 1.4

Signed and sealed this 22nd day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A PROCESS FOR THE FLOTATION SEPARATION OF WAXY HYDROCARBONS FROM WAXYOILS TO PRODUCE DEWAXED OIL HAVING REDUCED CLOUD AND POUR POINT WHICHCOMPRISES PASSING A FLOTATION GAS UPWARDLY THROUGH THE WAXY OIL WHICHHAS BEEN COOLED TO A TEMPERATURE BELOW ITS CLOUD POINT, SAID WAXY OILCONTAINING PROPORTION OF CRACKED MATERIAL FROM 0.5 TO 100% VOLUME ANDHAVING A VISCOSITY, AT THE SEPARATION TEMPERATURE, OF NOT MORE THAN 20CENTISTOKES WITH THE MAXIMUM VISCOSITY RANGE BEING 20 CENTISTOKES WHENUSING 100% OF CRACKED MATERIAL TO 15 CENTISTOKES WITH 2% CRACKEDMATERIAL; SAID GAS TREATMENT PRODUCING A WAX-CONTAINING FOAM LAYER AND ADEWAXED OIL LAYER, AND SEPARATING THE DEWAXED OIL LAYER THEREFROM HAVINGREDUCED CLOUD AND POUR POINTS.